Method of forming concrete articles and slip forming machine therefor



D. H. DODD Aug. 10, 1965 MING CONCRETE ARTICLES AND SLIP FORMING MACHINETHEREFOR METHOD OF FOR 5 Sheets-Sheet 1 Filed April 4, 1963 R 0 T N E vN ATTORNEYS D. H. DODD Aug. 10, 1965 METHOD OF FORMING CONCRETE ARTICLESAND SLIP FORMING MACHINE THEREFOR 5 Sheets$heet 2 Filed April 4, 1963DAVID H. DODD Aug. 10, 1965 D. H. DODD METHOD OF FORMING CONCRETEARTICLES AND SLIP FORMING MACHINE THEREFOR 5 Sheets-Sheet 5 Filed April4, 1963 o m K FIG] INVENTOR DAVID H. DODD Eur ATTORNEYS Aug. 10, 1965 D.H. DODD METHOD OF FORMING CONCRETE ARTICLES AND SLIP FORMING MACHINETHEREFOR 5 Sheets-Sheet 4 Filed April 4, 1963 INVENTOR DAVID H. 0001) BY{gg WJJZEA ATTORNEYS Aug. 10, 1965 D. H. DODD 3,200,177

METHOD OF FORMING CONCRETE ARTICLES AND SLIP FORMING MACHINE THEREFORFiled April 4, 1963 5 Sheets-Sheet 5 FIGIZ v n 2 2 i a 242 i 240 K 25a254 FIG. l3

INVENTOR. DAVID H. 0000 A TTORNE Y6 United States Patent 3,200,177ME'IIIGD (BF FURMING CONERETE ARTICLE AND SLIP FQRMING MACHINE THEREFORDavid II. Budd, Gallatin, Tenn, assignor of one-half to Clarence Riegel,Nashville, Tenn. Filed Apr. 4, 1963, Ser. No. 270,643 26 Claims. Mil.264-70) This application is a continuation-in-part of the followingcopending application: Serial No. 643,360, filed March 1, 1957; SerialNo. 786,879, filed January 18, 1961; and Serial No. 99,754, filed March31, 1961, all of which are now abandoned.

This invention relates to a method for forming concrete articles and aslip forming machine and more particularly to a travelling vibratorymachine for molding elongated concrete structures, such as prestressedconcrete beams and the like.

In recent years, the use of prestressed concrete beams and structuralmembers has substantially increased until today prestressed concretestructures are used in a wide variety of applications as joists, joints,columns, beams, slabs, and similar articles. Heretofore, thesestructural members have been almost uniformly produced with equipmentnecessitating a substantial amount of hand labor. One example is thewell known method of casting prestressed concrete. beams in a pluralityof gang molds. These machines are necessarily slow in operationrequiring large quantities of time and effort from a number of highlyskilled laborers. In addition, complicated as sembly proceduresinvolving collapsible or disposable cores are necessary for formingcored concrete elements.

The present invention avoids the above-mentioned disadvantages byproviding a novel extrusion type slip-forming machine of improvedconstruction making it possible to produce elongated concrete structureswith approximate one-fourth the labor cost now experienced in knownmolding operations at roughly one-half or less the initial equipmentcost as compared with a conventional prestressing plant using fixedforms and collapsible cores.

While travelling type molding machines have been proposed, none has beencompletely satisfactory since those using a relatively wet concrete mixinvariably produce an article which tends to slump or completelycollapse and heretofore it has been impossible to provide sufiicientplasticity to the relatively dry or no-slump mixes so as to mold them tothe desired shape in a travelling type machine. The present inventionovercomes the difiiculties with wet mixes on the one hand and dry mixeson the other by providing a machine capable of greatly intensifiedvibrations, so as to impart a limited amount of plasticity to the verydry mixes of the type conventionally used in making concrete blocks.These intensified vibrations of approximately two or three times thepower previously used in vibrating machines are applied at the center ofpercussion of the top plate of the mold with its trailing edge as aneutral axis so that the vibrations, even though greatly intensified, donot interfere with the release of the product at the trailing edge ofthe mold. Through the use of these intense vibrations in conjunctionwith the novel mold forms and cores constructed in accordance with thepresent invention it is possible to form a homogeneous product in spiteof the limited amount of plasticity which can be imparted to the dry mixmaterial.

Important features of the present invention in addition to the above,include the provision of a main mold vibrated by an eccentric rotatingabout an axis perpendicular to the direction of machine travel and theprovision of mold cores which are similarly vibrated.

It is, therefore, one object of the present invention to provide a novelextrusion type slip forming machine for elongated concrete structures.

Another object of the present invention is to provide a novel moldconstruction for an extrusion type slip form ing machine.

Another object of the present invention is to provide a self-propelledslip forming machine suitable for use with relatively dry concretemixes.

A still further object of the present invention is to provide a slipforming machine having an improved core arrangement.

Another object of the present invention is to provide a moldconstruction particularly suited for use in conjunction with a pluralityof vibrating cores.

These and further objects and advantages of the invention will be moreapparent upon reference to the following specification, claims andappended drawings, wherein:

FIGURE 1 is an elevational view of the overall slip forming machine ofthe present invention.

FIGURE 2 is an elevational view of the mold and cores incorporated inthe machine of FIGURE 1.

FIGURE 3 is a plan view of the machine of FIGURE 1.

FIGURE 4 is a front end view of the novel machine of FIGURE 1.

FIGURE 5 is a rear end view of a portion of the machine of FIGURE 1.

FIGURE 6 is an elevation showing one of the mold cores incorporated inthe machine of FIGURE 1.

FIGURE 7 is a front view of the machine of FIGURE 1 with the corevibrating assembly removed.

FIGURE 8 is a cross section taken along line 88 of FIGURE 3.

FIGURE 9 is a horizontal section taken along line 9-4 of FIGURE 6.

' FIGURE 10 is a vertical section taken along 16-18 of FIGURE 9.

FIGURE 11 is a cross section through the resulting product emerging fromthe rear end of the machine of FIGURE 1.

FIGURE 12 is an elevational view of the stabilizing frame at the frontend of the machine.

FIGURE 13 is a plan view of the stabilizing frame.

FIGURE 14 shows a pair of movable cable guide hooks at the front of themachine.

FIGURE 15 is a view similar to FIGURE 14 showing the hooks moved intocable engaging position; and

FIGURE 16 shows a divider assembly useable in conjunction with themachine of this invention.

Referring to the drawings and particularly FIGURES 1 through 3, thenovel slip forming machine of the present invention generally indicatedat It) is of the self-propelled type and is adapted to move over anelongated concrete runway or other support indicated at 12. In theseveral figures of the drawings, various portions are shown broken awayand minor details have been omitted for the sake of clarity. Only theimportant novel elements of ltflhe rlnachine of the present inventionare described in etai The slip forming machine It is propelled by asuitable motor 14 mounted on a support 16 over the rear end of themachine and connected by a chain belt 18 to a pulley 20. The shaft 22upon which pulley 20 is mounted carries a smaller pulley 24 receiving adrive chain 26 passing over an idler pulley 28 and driving front wheels3% and rear wheels 32.

The wheels support a generally rectangular frame having fiat horizontalside frames 34 and as provided with depending vertical skirts 38 and 4%which cover the wheels and which are provided with suitable bearingsreceiving the wheel axis. Supported on the side frames 34 and 36 is aframework generally indicated at 42 which in turn supports a hopper 44for feeding a relatively dry concrete mix into the machine.

Attached to the upper surface of side frames 34 and line 36 midway ofthe ends of the machine are four upright channels 46 which are slottedto slidably receive guide blocks 48. These guide blocks form avertically adjustable support for the entire mold assembly generallyindicated at 50 and shown in FIGURE 2.

Threadedly received in each of the guide blocks 48 is a screw 52rotatably driven by a cross shaft 54 shown in FIGURE 8 having a wormgear 56 at each end and received in the gear box 58 supported on thechannels 46. The upper unthreaded end of each screw 52 is rotatablyreceived in a pipe 60 attached to the top of gear box 58 and carries agear 62 meshing with the worm gear 56. In this manner by suitablydriving the cross shaft 54 the four screws 52 are rotated in unison inthe appropriate directions to raise and lower the guide blocks 48 andhence the entire mold assembly.

Mova'bly carried by the guide blocks 48 are a pair of side plates 64 and66. Each of the side plates is provided with a support block 68 uponwhich is resiliently mounted the mold framework generally indicated at70. The mold framework is provided with brackets such as 72 connected tothe support blocks 68 by rubber or other solid resilient support blocks74. Thus, upward and downward movement of the guide blocks 48 by meansof the rotational movement of the screws 52 acts to raise and lower theentire mold assembly 50.

A pair of brackets 76 and 78 formed integral with the side plates 64 and66 pivotally receive a cross bar 80 to which is connected an adjustablemotor mounting plate 82. Secured to the plate 82 by a bracket 84 is amotor 86 coupled by a pulley 88 to a horizontal transverse shaft 90.Shaft 90 is supported in a plurality of bearings 92 and carries aplurality of eccentric weights such as 94. The motor mount is providedwith an adjustable screw 96 bear-ing against a plate 98 so that thetension on pulley 88 can be adjusted by adjustment of the screw 96 so asto pivot the entire motor mount about the pivots 80.

The mold framework 70 is provided with a plurality of apertures 98 inits top surface and is attached to the mold proper 100. In this way,rotation of the shaft 90 carrying the eccentric weights causes both themold and framework supported by the resilient blocks 74 from the sideplates 64 and 66 to vibrate with the eccentric weights. An importantfeature of the invention is that the eccentric weights are located suchthat the top plate of the mold is vibrated at its center of percussionwith respect to its trailing edge as a neutral axis. The direction ofmachine travel is indicated by the arrow in FIGURE 1.

Referring especially to FIGURE 3, the mold 100 comprises a main mold 102and a trailing mold 104. Main mold 102 is made of two parts which areadjustably but rigidly interconnected to form a single main moldelement. The curved top plate 106 of the front section 108 of the mainmold is provided with a pair of vertical brackets 110 and 112 at itsrear end which engage in overlapping relation similar brackets 114 and116 extending upwardly from the rear section of the main mold. Thesebrackets are provided with aligned apertures pivotally connected at 120.The rear section brackets 114 and 116 are also provided with anelongated arcuate slot as at 122 which is in alignment withcorresponding apertures in the brackets 110 and 112 and which arerigidly connected by suitable bolts. In this way, the rear section 1 18of the main mold may be slightly adjusted with respect to the frontsection 108 of the main mold.

Referring to FIGURES 1 through 3 and especially to FIGURE 2 the rearsection 118 is provided with a framework 124 on its outer surfaceincluding a vertical plate 126 on each side which receives one end of apull bar or rod 128 connecting the main mold to the trailing orfinishing mold 104. This latter mold is provided with a similar externalframework 130 including a similar vertical plate 132 receiving the otherend of pull bar 128.

Referring particularly to FIGURES 2, 3 and 5, the trailing mold is madeof three sections comprising a top plate 133 and two side plates 135 and137. Rigidly sei cured to each of the side plates are verticalattachments 134 and 136 provided with inwardly projecting lugs 139 and141 which define the recessed upper edges 143 and 145 as well as thegrooves 147 and 149 in the resulting concrete structure illustrated inFIGURE 11.

A pair of resilient rubber blocks 142 and 144 are provided with bolts138 and 140 for attachment to a pair of plates 151 and 153 secured tothe machine frame. Rubber blocks 142 and 144 are mounted on and securedto a transversely extending angle iron 146 attached to top plate 133.The vertical flange 148 of the angle iron receives the ends of .a pairof pull rods whose other ends are bolted to brackets 152, secured to thetop of the rear end of the main mold. Thus the only direct connectionbetween the main mold and the trailing or finishing mold 104 is by wayof the four pull rods 128 and 150.

Passing through the interior of both the main and trailing molds arethree hollow cores 150, 152 and 154. The front ends of each of the coresare secured by bolts as at 156 and 158 (FIGURES 4 and 6) to upper andlower flanges 160 and 162 formed on a front plate 164. Secured to thefront plate 164 by a pair of bearings 166 is a horizontal shaft .168carrying a plurality of eccentric weights 170. One end of shaft 168carries a pulley wheel 172 adapted to be driven by a suitable pulleyarrangement (not shown) from the motor 86. Secured to the frame of themachine by a pair of bolts 174 and 176 are a pair of mounting brackets178 and 180 which brackets carry rubber or resilient blocks 182 forresiliently supporting the front plate 164. In this way the front plateis resiliently mounted so that it and the cores which it supportsvibrate in conjunction with the rotation of the eccentric weights 170.

Referring to FIGURE 7 which shows part of the mold with the front plate64 and vibrator structure removed, the front end of the mold is closedoff by a front plate provided with three channels 192 through which passthe cores 150, 152 and 154. Front plate 190 is provided with eightapertures 193 through which pass prestressed reinforcing wires or cables194 imbedded in the resulting concrete product 196 as illustrated inFIGURE 11 which is a cross section through the product as it emergesfrom the rear end of the machine of this invention. As can be seen fromFIGURE 11, the cores leave central cavities 198, 200 and 202 in theproduct.

Each of the cores as best seen in FIGURE 6 is formed of a main section204 and a trailing or finishing section 206. Referring to FIGURES 9 and10, a central vertical plate 208 is secured to the main core section 204by a side plate 210. Secured to the rear end of vertical plate 208 is anelongated rod or weight 212 extending outwardly beyond the rear end ofthe mold core.

The rear core section 206 is resiliently supported from the main section204 by a pair of rubber blocks 214 and 216, each secured to the centerplate 208 attached to the main core section 204. Rear rubber block 216is bolted to a vertical plate 218 in trailing section 206. Verticalplate 208 is provided with a cut out or aperture 220 through whichpasses a horizontal bar 222 supported by flanges 224 and 226 on trailingsection 206. Rubber block 214 is bolted to bar 222 and is attached atits other side to a bracket 228 secured to the center plate 208 at oneend of the cut out 220.

FIGURES 12 and 13 show the stabilizing frame 240 for guiding the machine10 along the prestressed reinforcing cables 194. While the frame 240 isnot essential to operation it greatly increases the ability of the slipforming machine to following an accurate path along the bed 12 and helpsto prevent fish tailing during the machine travel.

Frame 240 comprises a pair of elongated arms 242 and 244 pivoted tobrackets 246 and 248 mounted on the machine frame. Arms 244 are joinedby a cross bar 250 preferably positioned about eight feet from the frontof the machine. The outer ends of the arms carry small wheels 252 and254 and a transverse rod 256 to which are secured a pair of cable guides2.53 and 26b in the form of eyelets or hooks. The lower outermost cables1% are threaded through the cable guides.

Attached to the front end of the machine between arms 242 and 248 is aparallelogram type lever assembly 261 carrying a pair of cable guidehooks 2*32 and 264. The lever assembly is pivoted to the machine frameat 26c and 263 so that movement by a suitable actuator handle (notshown) causes the assembly to pivot from the position illustrated inFIGURE 14 to that of FIGURE 15 so that the hooks 262 and 264 movelaterally and upwardly into engagement with the same cables passingthrough guides and 260.

In operation, the machine of the present invention is self-propelled ona suitable fiat bed 12 such as a concrete runway or the like. Relativelydry mix of the no-slump variety carried in the hopper 44 passesdownwardly into the mold where it is vibrated, compacted and formed intothe shape of the resulting article. By means of the shaft 74 transverseto the direction of motion of the machine indicated by the arrow inFIGURE 1 itis possible to apply very powerful vibrations to therelatively dry mix so as to impart suficient plasticity thereto to formthe concrete mix into the desired shape and to sufiiciently compact it.This mix is relatively dry so that it does not require any long trailingmolds and is self-supporting as it emerges from the rear end of themachine.

An important feature of this invention is the fact that the vibrationsare applied to the top plate of the mold at its center of percussionwith respect to its trailing edge as a neutral axis. Thus, while verypowerful vibrations may be applied by the eccentric weights to the topof the mold, the vertical components of this vibration diminish alongthe length of the mold so as to substantially disappear at the rear edgeof the main mold. Since the sides of the main mold (as distinguishedfrom the trailing mold) are rigidly connected to the top plate theylikewise undergo little or no vertical vibration at their trailingedges. As distinguished from the vertical components of motion impartedby the eccentric weights on shaft '74 the horizontal components do notdisappear and exist along the entire length of the mold.

Trailing mold TM is secured to the machine frame through a resilientmounting and is only coupled to the main mold by the pull bars 128 and15%. In this way the horizotnal component of motion is transmitted tothe finishing mold so as to provide a smoothing or planing action to thesurface of the material just before it emerges from the rear edge of themachine. This horizontal pull bar coupling further assures that anysmall vertical components of motion that may exist at the rear edge ofsection lilb are not transmitted to the trailing mold since they wouldtend to disturb and disrupt the shape of the material as it emerges fromthe rear end of the machine.

A further important feature of the slip forming machine of the presentinvention involves the gradual diminishing shape of the main mold inconjunction with the gradually diminishing convex channels illustratedat 23% and 232 in FIGURES 2 and 7. This particular shape provides alifting and compacting of the vibrating mix material in the mold andassures proper disposition of mix beneath the prestressed reinforcingcables 1% extending along the upper side of the mold. As is well known,when mix is under vibration there is a certain amount of naturalcompacting due to the force of gravity which tends to leave cavities orair pockets beneath reinforcing cables passing through the concretematerial. The gradual taper of the mold in conjunction with the channelsassists in this gravity compacting and imparts a centralizing andpartial lifting force to the compacting material so as to assure flow ofconcrete into the pockets which might otherwise exist immediatelybeneath the upper reinforcing cables 1%.

A novel feature of the present invention is believed to reside in theprovision of a machine for producing core-d concrete structures whereinthe cores are also vibrated at their center of percussion with respectto their trailing edge as a neutral axis. The resilient mounting at therear end of the main core section 2% in conjunction with the extendedbars or weights 212 makes this possible. These bars 212 constitute aweighted extension on the end of the main core section 2-534 tocompensate for the fact that the cores are vibrated by eccentric weightsM6 connected to brackets 11% positioned in front of the cores. As iswell known, the center of percussion of a flat plate is approximatelytwo-thirds of the overall length of the plate from the edge constitutingthe neutral axis. In view of the vibration of the cores from beyond theleading edge of the core, the necessary result is that the trailingweights 212 under-go a certain amount of vibration but these arepositioned well away from the concrete material towards the center ofthe cores and make it possible to neutralize the vertical components ofvibration in the cores at the desired point, i.e., at the rear edge ofmain core section 2G4. Because of the resilient mounting of the trailingedge core section 2% to the main core section 2% any small verticalcomponents of vibration which might exist are not imparted in anysignificant magnitude to the trailing core 296.

The specific shape of the main mold has been found to be quite importantbecause of the limited plasticity of the relatively dry aggregate and inlight of the discovery that large portions of the aggregate tend to bedrawn by friction along the top and side surfaces of the mold as ittravels. Specifically, it has been found necessary to provide the frontof the mold with a disproportionately increased cross section near theupper surface of the mold. The result is that there is adisproportionate excess of aggregate near the top of the mold whichdisproportionality gradually decreases as the channel sections 23% and232 diminish. It is apparent that because of the increased cross sectionat the front of the mold and the gradual reduction in both the height ofthe mold and the cross sectional area at the top, most of the compactingand forming is accomplished at the front end of the mold, approximatelythrough the front one-third of the mold, which is the approximateextension of the channels 23.) before their disappearance into thevertical mold sides. The overall width of the mold is constant along itsentire length.

This curvature or taper of the mold because of the majority ofcompacting taking place the first one-third of the mold length must beat least a third order magnitude or higher curve. Applicant has foundthrough testing various factors that affect mold compaction that thedifficulties heretofore encountered, particularly in forming the uppercorners of the mold product, are eliminated by this construction.

The trailing edge of the non-vibrating support sections 2% of the coresare exact product form which is slightly smaller than the trailing edgeof the main core sections 264. The trailing sections 2536 aresubstantially completely free of any vibration due to the resilientmounting previously described. The rearward end of the vibrating part ofthe cores is preferably positioned at or near the rearward end of thevibrating trailing mold. Otherwise, there is a tendency to shaking downof the material. As a result, section 2% of each core projects outwardlyslightly beyond the rear end of the trailing mold. The rear side platesof the trailing mold which do have a horizontal vibration parallel tothe machine bed project somewhat beyond the top plate of the trailingmold as a support for the sides of the product. These features all helpto pr vent slumping of the product due to internal product vibrationsome distance beyond the inducing vibrations of the main mold. Thisdistance, however, due to the dry nature of the mix is substantiah lyreduced and forms only a small fraction of the overall machine length.

In addition to its primary function of producing elongated concrete coreelements, the machine of the present invention may be utilized to formreinforced solid products. For example, a smaller version of the machineof the present invention may be utilized to form reinforced concrete 1beams. FIGURE 12 shows a divider structure suitable for use inconjunction with an I beam forming machine constructed in accordancewith the present invention wherein the machine travels along the lengthof pretressing rods such as the vertically spaced rods 240 of FIGURE 12.In such an arrangement a skeleton spacer 242 may be positioned at anylocation where it is desired to terminate an individual concrete elementand this skeleton spacer may be backed up at a slight distance furtheralong the direction of travel of the machine by a solid spacer 244. Theskeleton nature of the spacer 242 assures that the mix material draggedalong the machine will not be seriously disrupted in front of the spacer242 but will be able to continue to flow along through the apertures246. The spacers 242 and 244 are connected by a pair of stiff rods 248and these are held to the runway bed or base by a nut threaded over abolt 2.52 imbedded in the base. A shield 254- is positioned between thespacers to shield the prestressing cables 240.

When the machine has passed over the spacers, the shield may be removedand the concrete material dug out to provide a terminal point for theend of a concrete beam or the like. For cored structures or in caseswhere dividers are not used, the elongated concrete structures areconventionally cut to length by suitable abrasive saws.

It is apparent from the above that the present invention provides anovel slip forming machine for constructing elongated concrete articlesof various types. The machine of the present invention overcomes thedifiiculties inherent in earlier machines wherein the concrete waseither too wet to be self-sustaining and tended to slump when exitingfrom the machine, or was so dry as to be incapable of being plasticizedand shaped by ordinary vibrating techniques. The present inventionovercomes these seemingly irreconcilable problems by providing center ofpercussion vibration to a relatively dry mix so that vibrations two orthree times more powerful than those previously utilized may be appliedto the material while at the same time maintaining the trailing edge ofthe top surface of the mold as a neutral axis so that verticalcomponents of vibration of the-top plate are completely eliminated oreffectively minimized. The device of the present invention isparticularly suited for producing cored structures. The machine isself-propelled and is guided by prestressing wires or cables stretchedalong a suit-able base. These cables become imbedded in the concretematerial and form a part of the finished structure. Both the main moldand the main core sections are vibrated at their centers of percussionwith respect to their trailing edges as a neutral axis, thusnecessitating only very short trailing or finishing sections on both themold and cores.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The presentembodiments are therefore to be considered in all respects asillustrative and not restrictive, the scope of the invention beingindicated by the appended claims rather than by the foregoingdescription, and all changes which come within the meaning and range ofequivalency of the claims are therefore intended to be embraced therein.

What is claimed and desired to be secured by United States LettersPatent is:

1. A slip forming machine comprising a mold having top and side walls,means for propelling said mold, and means for vibrating the top wall ofsaid mold at its center of percussion with respect to its trailing edgeas a neutral axis.

2. A slip forming machine comprising a mold having top and side walls,means for propelling said mold, an

eccentric carrying shaft mounted on said mold, and means for rotatingsaid shaft about an axis perpendicular to the direction of travel ofsaid mold, said shaft being mounted at the center of percussion of saidtop wall of said mold with respect to its trailing edge as a neutralaxis.

3. A slip forming machine comprising a mold, means for propelling saidmold, a core positioned within said mold and spaced from the mold walls,said core being supported from the front end of said mold, and means forvibrating said core at its center of percussion with respect to itstrailing edge as a neutral axis.

4. A slip forming machine according to claim 3 wherein said mold isvibrated at its center of percussion with respect to its trailing edgeas a neutral axis.

5. A slip forming machine comprising an elongated self-propelledtraveling mold having top and side walls, a hopper for concrete mixcarried near the front of said mold, an eccentric weight carrying shaftmounted at the center of percussion of the top wall of said mold withrespect to its trailing edge as a neutral axis, means for rotating saidshaft about a horizontal axis perpendicular to the direction of travelof said mold, a mold core supported within said mold from a point infront of said hopper and means for vibrating said core about its centerof percussion with respect to its trailing edge as a neutral axis.

6. A slip forming machine according to claim 5 wherein said coreincludes a weighted mas extending beyond its trailing edge and aneccentric rotating weight mounted on said core in front of said hopper.

7. A slip forming machine according to claim 6 including a shorttrailing section spaced from and behind said core, said trailing sectionbeing of final product form and size, and resilient means coupling saidtrailing section to said mass whereby said trailing section is isolatedfrom the vibrations of said mass.

8. A slip forming machine according to claim 7 wherein said eccentricrotating weight on said core is mounted on a rotating shaft having ahorizontal axis of rotation perpendicular to the direction of travel ofsaid machine.

9. A slip forming machine according to claim 8 including a plurality ofvibratory cores within said mold.

10. A slip forming machine comprising an elongated self-propelledtraveling mold, a hopper for concrete mix carried near the front of saidmold, said mold including top and side walls, an eccentric weightcarrying shaft mounted at the center of percussion of the top wall ofsaid mold with respect to its trailing edge as a neutral axis, means forrotating said shaft about a horizontal axis perpendicular to thedirection of travel of said mold, a plurality of spaced mold coressupported within said mold from a point in front of said hopper, ahorizontal shaft carrying an eccentric weight connected to the frontends of said cores, said core connected shaft rotating about an axisperpendicular to the direction of travel of said mold, said coresincluding top, bottom and side walls, the side walls of said corestapering outwardly beneath said hopper whereby the spaces between thetapering walls of adjacent cores meter the feed of mix to the bottom ofsaid mold, and a weighted mass mounted on each of said mold cores andextending outwardly beyond the ends of said cores, whereby said coresare vibrated about their centers of percussion with respect to theirtrailing edges as neutral axes.

11. A slip forming machine according to claim 10 including a shorttrailing section spaced from and behind each core, said trailingsections being of final product form and size, and resilient meanscoupling said trailing sections to said weighted mass whereby saidtrailing sections are isolated from the vibrations of said mass.

12. A mold for travelling vibratory machines comprising a top plate,means for vibrating said top plate about its center of percussion withrespect to its trailing edge as a neutral axis, and a pair of verticalside walls rigidly secured to said top plate, said top plate and saidside walls forming the top and sides of a mold, said top plate beingcurved to provide said mold with a greater vertical height at its frontend and a gradually reduced height toward its rear, said curve being atleast a third order function of the distance from the front of saidmold.

'13. A mold for travelling vibratory machines comprising a mold cavitydefined by a top wall and a pair of vertical side walls extending intoclose proximity to a mold surface, said cavity being open at both ends,and means for vibrating said top wall about its center of percussionwith respect to it trailing edge as a neutral axis, said side walls atone end of said cavity having a greater width across the top than at thebottom edges, said greater width gradually decreasing along the lengthof said mold until the width across the top of said mold at the otherend is less than at the bottom edges, said bottom edge width beingconstant along the length of said mold.

14. A mold according to claim 13 wherein said top wall is curved toprovide said mold with a greater vertical height at its front end and agradually reduced height toward its rear, said curve being at least athird order function of the distance from the front end of said mold.

15. In a travelling machine having a supporting frame including a pairof uprights, a mold resiliently supported from said uprights, said moldincluding top and side walls, means for vibrating said top wall at itscenter of percussion with respect to its trailing edge as a neutralaxis, and means sealing the bottom edge-s of said side walls against theescape of aggregate.

16. Apparatus according to claim 15 wherein said sealing means isresiliently urged against the bed over which said machine travels.

17. Apparatus according to claim 16 wherein said mold is verticallyadjustable.

18. A slip forming machine comprising a frame, means mounted on saidframe for propelling it along a flat bed, a plurality of verticalstandards mounted on said frame, a pair of side plates adjustablysupported by said standards, a main mold having rigidly connected topand side walls resiliently supported by said side plates and forming amain mold cavity, said cavity being open at both ends, said top wallbeing curved to provide said mold with a greater vertical height at itsleading end and a gradually reduced height toward its rear, said curvebeing at least a third order function of the distance from the leadingend of said main mold, a hopper for concrete mix carried by said framenear the leading end of said main mold, an eccentric weight carryingshaft mounted at the center of percussion of the top wall of said mainmold with respect to its trailing edge as a neutral axis, means forrotating said shaft about a horizontal axis perpendicular to thedirection of travel of said main mold, means supported by said frame forengaging prestressing cables passing through said main mold to guidesaid frame along said bed, a trailing mold rigidly coupled to said mainmold solely by a plurality of pull bars extending parallel to thedirection of travel of said main mold, a plurality of spaced hollow moldcores supported within said main mold from a point in front of saidhopper, a shaft carrying an eccentric weight connected to the leadingends of said cores, said core connected shaft rotating about an axisperpendicular to the direction of travel of said main mold, said coresincluding top, bottom and side Walls, the side walls of said corestapering outwardly beneath said hopper 'whereby the spaces between thetapering Walls of adjacent cores meter the feed of mix to said mainmold, each core including .a trailing section resiliently coupledthereto, a weighted mass mounted on each of said cores and extendingoutwardly beyond the ends of said core trailing sections, whereby saidcores are vibrated about their centers of percussion with respect to therear edge of their top walls as neutral axes.

19. A machine according to claim 18 including a cable guide framepivoted to the leading end of said frame, a

pair of wheels for supporting said cable guide frame over said bed, andcable guides mounted thereon approximately eight feet from said framefor engaging said pres-tressing cables to prevent fish-tailing of saidframe.

20. A machine according to claim 19 including a pair of cable engaginghooks mounted on said frame, and means for moving said hooks upwardlyand laterally of said frame to engage the undersides of prestressingcables passing through said main mold.

21. A molding bed for use with continuous extrusion type moldingapparatus for compacting .and shaping elongated concrete structures inend to end relationship, comprising a supporting base, at least oneprestressing cable positioned over said base, a skeleton body having theoutline of the cross sectional configuration of said concrete structureto be formed positioned around said cable, and means for anchoring saidskeleton body to said base at a predetermined division point at the endof one of said concrete structures, whereby said body protects the endedge of said one concrete structure from breakage as said structure isseparated from other adjacent structures by removing excess concrete atthe ends thereof, said skeleton body member having sufiicient spacebetween components to permit relatively unimpeded flow of concretetherethrough to compact around the reinforcing element passing throughsaid skeleton body.

22. Apparatus according to claim 21 including a pair of said skeletonbodies in parallel spaced relation providing sufficient dig-out spacetherebetween.

23. Apparatus according to claim 22 including a slipover tunnel-shapedshield for excluding concrete from the space between adjacent skeletonbodies corresponding to the location of said cable, and spacer andhold-down means for said bodies for facilitating the digging out ofconcrete at the ends of said structures.

24. A method of forming concrete articles comprising introducing arelatively dry concrete mix into a main traveling mold, and vibratingsaid mold about its center of percussion with respect to its trailingedge as a neutral axis whereby a limited amount of plasticity isimparted to said dry mix for forming in said mold.

25. A method according to claim 24 including vibrating a core Withinsaid mold about its center of percussion with respect to its trailingedge as a neutral axis.

26. A method of forming concrete articles comprising compacting andshaping a relatively dry mix between a pair of forms vibrated abouttheir centers of percussion with respect to one of their edges as aneutral axis, moving said forms, feeding fresh mix into the spacebetween said forms, and releasing the compacted and shaped mix from thesaid edges of said forms.

References Cited by the Examiner UNITED STATES PATENTS 1,920,716 8/33Schafer. 2,225,015 12/40 Lebelle 25-118 XR 2,818,790 1/53 Canfield etal. 25-32 2,938,255 5/60 Oakden 2532 FOREIGN PATENTS 151,075 4/53Australia.

158,013 8/54 Australia.

751,997 7/33 France.

818,955 6/ 37 France.

516,135 5/44 Great Britain.

700,947 12/ 5 3 Great Britain.

713,256 8/54 Great Britain.

793,942 4/ 5 8 Great Britain.

147,487 .10/54 Sweden.

OTHER REFERENCES Gessner: German application, 1,008,180, printed May 9,1957.

WILLIAM J. STEPHENSON, Primary Examiner. 3 MICHAEL v. BRINDISI,Examiner.

1. A SLIP FORMING MACHINE COMPRISING A MOLD HAVING TOP AND SIDE WALLS,MEANS FOR PROPELLING SAID MOLD, AND MEANS FOR VIBRATING THE TOP WALL OFSAID MOLD AT ITS CENTER OF PERCUSSION WITH RESPECT TO ITS TRAILING EDGEAS A NEUTRAL AXIS.